Quenching of Fluorescence of Chloropentafluoroacetone by Saturated Hydrocarbons

1972 ◽  
Vol 50 (9) ◽  
pp. 1429-1432 ◽  
Author(s):  
A. J. Yarwood
Keyword(s):  
Gas Phase ◽  
Rate Constants ◽  
Singlet State ◽  
Fluorescence Yield ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Quenching Rate ◽  
Saturated Hydrocarbons ◽  
Phase Measurements ◽  
Electronically Excited

Saturated hydrocarbons can quench the electronically excited singlet state of a simple ketone in the gas phase. Measurements on the quenching of the fluorescence yield of chloropentafluoroacetone at 23 °C show that different saturated hydrocarbons can deactivate the excited singlet state with varying efficiencies. The quenching rate constants are reported and possible relationships considered.

The Excited Singlet State of Chloropentafluoroacetone; Quenching by Unsaturated Hydrocarbons

1971 ◽  
Vol 49 (12) ◽  
pp. 2053-2058 ◽  
Author(s):  
H. S. Samant ◽  
A. J. Yarwood
Keyword(s):  
Gas Phase ◽  
Singlet State ◽  
Excited Singlet State ◽  
Energy Relation ◽  
Excited Singlet ◽  
Quenching Rate ◽  
Unsaturated Hydrocarbons ◽  
Linear Free Energy ◽  
Free Energy Relation ◽  
A Charge

The fluorescence of chloropentafluoroacetone in the gas phase at 23 °C is quenched by the addition of certain olefins. The quenching rate constants of 17 unsaturated hydrocarbons for the first excited singlet state of chloropentafluoroacetone are reported. The molecules are divided into two classes on the basis of their quenching abilities, (a) olefins with only electron-withdrawing substituents and (b) olefins with electron-donating substituents. It is shown that the quenching by molecules in the latter group can be quantitatively correlated with the ionization potential (i.p.) of the quenching molecule. The relation is log k = 18.0 − 0.79 (i.p.), i.e. a type of linear free energy relation is obeyed. This implies that the quenching by molecules containing only electron-donating substituents involves a charge-transfer complex.

Combined Experimental and Theoretical Study of the Transient IR Spectroscopy of 7-Hydroxyquinoline in the First Electronically Excited Singlet State

2016 ◽  
Vol 120 (47) ◽  
pp. 9378-9389 ◽  
Author(s):  
Felix Hoffmann ◽  
Maria Ekimova ◽  
Gül Bekçioğlu-Neff ◽  
Erik T. J. Nibbering ◽  
Daniel Sebastiani
Keyword(s):  
Ir Spectroscopy ◽  
Theoretical Study ◽  
Singlet State ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Electronically Excited

The structure, photochemical reactivity, and photophysical properties of adamantyl X-substituted aryl ethers and a comparison with the alkyl groups, methyl, tert-butyl, and allyl

2005 ◽  
Vol 83 (9) ◽  
pp. 1237-1252 ◽  
Author(s):  
A L Pincock ◽  
J A Pincock
Keyword(s):  
Excited State ◽  
Rate Constants ◽  
Singlet State ◽  
Bond Cleavage ◽  
Photophysical Properties ◽  
Excited Singlet State ◽  
Quantum Yields ◽  
Aryl Ether ◽  
Excited Singlet ◽  
Aryl Ethers

The structure, photophysical properties, and photochemistry of the adamantyl aryl ethers 1 in both methanol and cyclohexane have been examined. UV absorption spectra, 13C NMR chemical shifts, X-ray structures, and Gaussian calculations (B3LYP/6-31G(d)) indicate that these ethers adopt a 90° conformer in the ground state. In contrast, fluorescence spectra, excited singlet state lifetimes, and calculations (TDDFT) indicated a 0° conformer is preferred in the first excited singlet state S1. Irradiation in either solvent results in the formation of adamantane and the corresponding phenol as the major products, both derived from radical intermediates generated by homolytic cleavage of the ether bond. The 4-cyano substituted ether 1j was the only one to form the ion-derived product, 1-methoxyadamantane (16% yield), on irradiation in methanol. Rate constants of bond cleavage for these ethers from S1 were estimated by two different methods by comparison with the unreactive anisoles 2, but the effect of substituents was too small to determine structure–reactivity correlations. The temperature dependence of the quantum yields of the fluorescence of the unsub stituted, 4-methoxy and 4-cyano derivatives of 1 and 2 were also determined. These results indicated that the activated process for 1 was mainly bond cleavage for the 4-cyano substrate whereas for 2, it was internal conversion and intersystem crossing. Key words: aryl ether photochemistry, fluorescence, excited-state rate constants, excited-state temperature effects.

Violation of Hund's multiplicity rule in the electronically excited states of conjugated hydrocarbons

1985 ◽  
Vol 63 (7) ◽  
pp. 1572-1579 ◽  
Author(s):  
Shiro Koseki ◽  
Takeshi Nakajima ◽  
Azumao Toyota
Keyword(s):  
Triplet State ◽  
Excited States ◽  
Singlet State ◽  
Basis Set ◽  
Excited Singlet State ◽  
Excited Singlet ◽  
Electronically Excited States ◽  
Conjugated Hydrocarbons ◽  
Electronically Excited ◽  
Linear Polyenes

Violation of Hund's multiplicity rule in the electronically excited states of conjugated hydrocarbons is studied by using the Pariser–Parr–Pople type SCF MO method and the abinitio MO method with STO-3G basis set, both methods being augmented by CI-type treatments. It is shown that for symmetrical structures (D2h) of the nonalternant hydrocarbons, propalene, pentalene, and heptalene, the lowest excited singlet state is energetically lower than the corresponding triplet state. This is mainly due to the spin polarization (SP) effects. For D2h, structures of pentalene and heptalene the open-shell excited singlet state is predicted to be lower in energy than the closed-shell state, with the result that the former is really the ground state. Further, calculations made by including electron correlation effects reveal that in linear polyenes and polyacenes, the lowest excited singlet "minus" state (using Pariser's classification of the alternancy symmetry species) is lower in energy than the corresponding triplet state. The energy lowering of the singlet "minus" state in linear polyenes is due mostly to the mixing with the doubly excited configurations (mm → nn), while the considerable part of it in polyacenes is due to the SP effects.

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